Origin
The Hardline movement grew out of the more politically conscious sections of the Southern California hardcore and punk scenes in 1990. Although one of the basic tenets of Hardline was that it had existed in various forms since the beginning of time, the ideology was largely formulated by Sean Muttaqi of the band Vegan Reich. The Hardline philosophy was said to be rooted in one ethic (the sacredness of innocent life), but in reality the ethos rested on that base and on an idea of an immutable Natural Order. Put in more specific terms, Hardline can be described as a synthesis of deep ecology, straight edge, animal liberation, leftism, and Abrahamic religion.
In practice, the Hardline philosophy forbade its adherents from smoking or chewing any form of tobacco, drinking alcoholic beverages, and using illicit drugs or modern medicines. Furthermore, Hardliners (as they were called) were expected to follow a strict dietary regimen based on the above-mentioned pillars of respect for innocent life and the "Natural Order." To that end, Hardliners ate only foods that were vegan and relatively natural (brown rice over white, evaporated cane juice over white sugar, organic produce over conventional, natural oils over hydrogenated, etc). Human rights issues were also factored into the movement's food politics, and followers were urged to shun third-world cash crops such as coffee, chocolate, sugar, and most tropical fruits. Hardliners included caffeine in their stance on mind altering drugs so the first two items were generally abstained from, but consumption of the last two (and especially the final) was often given more leeway.
In keeping with its Abrahamic view of the natural order, the sexual politics of the Hardline movement were very conservative. Pre-marital sex was frowned upon, homosexuality seen as anathema, pornography abjured, artificial contraception avoided, and abortion militantly opposed. The official Hardline stance on sex was that its natural purpose was purely procreative, but many hardliners played fast and loose with that idea and justified recreational sex within the context of committed relationships as "potentially procreative" by opting not use artificial contraceptives. Interestingly enough, Hardline was always highly syncretic (over time absorbing influences from anarchism, Islam, the Rastafari movement, and a host of other schools of thought) and initially attempted to give its obviously Biblical sexual morals added credibility by claiming a Taoist foundation for them. This appeal to the anti-Western, politically correct, orientation of the punk and hardcore scenes met with little success and the topics of abortion and homosexuality were always sources of tension between Hardliners and their subcultural cousins.

Hardline's relationship to straightedge is a complex one of give and take. When Vegan Reich briefly reformed in 1999, Muttaqi credited the movement with the spread of vegan straightedge ideals in the 1990s. Partially true, vegan straightedge came from 'Hardline'. Hardline was undoubtedly heavily inspired from its inception by straightedge. The original logo of the movement was an outline of a large "X" (the sign most often associated with straightedge) with two crossed M16 rifles inside of it. Additionally, Muttaqi has said in the past that he was first exposed to the idea of fusing veganism and abstinence from drugs by an English punk named Rat (of the bands Statement, Unborn, Talisman, and others). Unknown to most, Rat had coined the term "vegan straight edge" by the mid-1980s. Those with an interest in the history of hardcore music should note that this was years prior to Ray Cappo (singer for the band Youth Of Today) grafting vegetarianism and straightedge after his exposure to Krishna Consciousness. However, Rat was doing little to spread his ideology while Muttaqi was transforming and propagating it. Vegan Reich was many in the hardcore scene's first exposure to ideas about militant animal liberation and the controversy they aroused drew considerable attention to their positions. Those in the subculture who gravitated toward animal-related causes but disagreed with some of Hardline's finer points found themselves becoming vegan straightedge. Indeed, breakthrough vegan straightedge group Earth Crisis initially wanted Muttaqi to release their debut EP "All Out War" on his record label.
Essentially, vegan straightedge and Hardline had a co-genesis with the first birthing the second but the latter popularizing the former. But the complexity of Hardline's relation to straightedge does not end there. As the movement came into its own, many Hardliners decided that their philosophy was so beyond the narrow scene politics of straightedge that the two were entirely different things. The "X" was removed from the crossed rifles logo, straightedge was harshly criticized, and Hardliners were encouraged to leave behind the subcultural ghetto of the hardcore scene. Much of this sprang from the momentum being gained by the more activism oriented elements within the movement. Eventually Hardliners came to consider their network wholly divorced from the hardcore scene. The truth, however, was that the nature of information dissemination in a (mostly) pre-internet media environment made for recruiting from outside of the hardcore subculture next to impossible. Although Hardline served to involve people heavily in political activity, the overwhelming bulk of new members were straightedgers who would with time come to identify primarily as activists instead of hardcore kids.
History
The movement began to attract a fair number of followers of varying degrees of sincerity shortly after the 1990 release of Vegan Reich's "Hardline" EP and the official founding of the movement. Other bands soon formed; the most notable of them being Raid from Tennessee.
In fact, although Sean Muttaqi was still editing the zine "Vanguard" (Hardline's official press organ) and therefore exerting massive ideological influence on the movement, the center of its activities quickly shifted to Tennessee. Many in the Memphis hardcore scene adopted Hardline stances and started editing zines, organizing protests, engaging in direct action against industries that exploited animals, and otherwise acting on their new beliefs. Some of the most notable achievements of Memphis Hardline were organizing the movement's first annual Gathering, founding the long-standing and relatively mainstream Coalition To Abolish The Fur Trade (CAFT), and having a member (Frank Winbigler) win a state-wide power lifting competition.
As things began to fade in Memphis, and Sean converted to Islam and decided to leave the hardcore scene along with Hardline altogether, the movement was gaining attention and momentum in central Indiana. Not wanting the movement to die, but not wanting to be responsible for it either, Muttaqi transferred the editing of "Vanguard" over to a young resident of Indianapolis named Ryan Downey. Ryan put together a fair number of issues of the zine, sang for the bands Hardball and Warpath, and attempted to further move Hardline into the realm of mainstream political activism. After a few years of eating, breathing, and sleeping Hardline ("The General" once famously said that Hardline "allows for recreation" when asked by a new recruit if it was acceptable for followers to watch "Star Trek") Downey decided to devote some time to himself and his spiritual betterment (he had recently been exposed to the Bahá'í Faith through his progressive contacts). The "Vanguard" torch was thus passed to fellow Indianapolis Hardline member David Agranoff.
Under Agranoff's direction the movement made unprecedented inroads into activism outside of the punk and hardcore scenes. Hardliners were instrumental in CAFT, the Animal Defense League, and Vegans For Life. Some were also involved in Earth First!, anti-imperialist organizations, and other leftist causes and groups. Starting with Agranoff's Upstate Hardline chapter, some cells began making direct contact with the general public by hosting educational forums that were essentially lectures on current events but from Hardline's unique spiritual-political perspective. It was also during this period that the Hardline philosophy was refined and many of its stances on varying issues grew more nuanced.
Running parallel to, but largely outside of, Agranoff's current was an attempt by some Hardliners from Massachusetts to establish an intentional community in Hawaii. The effort quickly failed due to personality conflicts (especially the ongoing debate among group members as to whether or not cooked food was natural enough) and a distinct lack of required agricultural and engineering skills.
In mid-1998 the movement experienced a massive internal upheaval as Sean Muttaqi returned to Hardline and with a group of new followers issued the eighth edition of "Vanguard" without warning Agranoff or the rest of the extant membership. "Vanguard" number eight announced the reorganization of the movement under the authority of the newly-created Hardline Central Committee (HCC) and castigated Agranoff and his comrades for softening the network's ideology through their refinement and development of it. Chapters were instructed to report to the Committee for evaluation and were told in no uncertain terms that they would not be recognized as cells until they submitted to this review. Also in the issue was a document about the stages through which the Hardline revolution would progress which was presented as being from 1990, but had never before been seen and was suspiciously contemporary feeling.
Many chapters (including Agranoff's) opted to leave Hardline entirely and instead established a new activist network called Education For A Sustainable Future (ESF). ESF differed from its predecessor in that it took no stances on sexual politics, was not a membership organization, and was entirely based in activism instead of subcultural activity. Much like Hardline, ESF had a holistic world view -- but it managed to skillfully avoid many of the old movement's pitfalls and could thereby successfully integrate itself into the greater progressive milieu.
Those who remained with the HCC steered Hardline in increasingly Islamic and Islamist directions for close to a year. After that, the Committee published "Vanguard" number nine which announced the formal dissolution of the movement. According to the zine, Hardliners would remain ideologically committed but would no longer act as an official organization and would instead function as an underground network of infiltrators into other revolutionary organizations, movements, and subcultures. This phase of the network's revolutionary plan was outlined in "Vanguard" eight.
It would appear that those Hardliners left standing decided that radical Islam was the tendency ripest for infiltration and almost immediately after the publication "Vanguard" nine founded Ahl-i Allah (The People Of Allah). The infant group's website featured old "Vanguard" articles that had been slightly rewritten to fit the organization's interpretation of Islam and new writings of a decidedly more Muslim bent. The Ahl-i Allah has since reorganized itself as the Taliyah al-Mahdi. In spite of both the Islamism of the new group and the critism contained in "Vanguard" eight of the affinity with neo-paganism the old movement developed during Agranoff's tenure, the Taliyah surprisingly continues the Hardline tradition of syncretism. The masthead of the group's website features Arabic writing, a yin-yang, I-Ching trigrams, and two crossed pieces of mediaeval Chinese weaponry. An essay the group distributes promoting veganism from a Muslim perspective is called "Live Ital," an obvious nod to Rastafarianism.
At its height, the Hardline movement had chapters all over the US, Europe, South America, and Australia.
Subcultural Activities
Among the bands who adhered to the Hardline ideology aside from Vegan Reich were Raid (Tennessee, US), Statement (UK), Recoil (Tennessee, US), Pure Blood (Tenessee, US), New Dawn (US), Uprising (New York, US), and Talisman (New York, US).
Bands with some Hardline members were Day of Suffering (North Carolina, US), Ecorage (Essen, Germany), Birthright (Indiana, US), Eighteen Visions (California, US), Abnegation (Pennsylvania, US), Absence (Italy), Força Vegan (BRA), Warcry (Indiana, US), Contempt (New York, US), Beta Minus Mechanic (New York, US), Race Traitor (Illinois, US), Framework (New York, US), Captive Nation Rising (California, US), Gatekeeper (New York, US), Sunrise (Poland), Pressure (California, US), Warpath (Indiana, US), Talisman (UK), Slavearc (UK), Path Of Resistance (New York, US), Hardball (Indiana, US), Pain Runs Deep (Poland), Healing (Poland) and The Farthest Man (New York, US).
Hardline publications included the zines "Praxis", "Destroy Babylon", "Contention Builder", "Declaration", "Unveil The Lies", "Defense, Rescue, Survival", "S.E.A.L." Straight Edge Animal Liberation, "Caring Edge", "Vanguard", "Eco War", "VoiceboX" and "Vision of Strength".
Whilst there has been no single, systematic criticism of Hardline it is essentially a form of deep ecology. Many of the arguments and standpoints of the Hardline are taken apart by Murray Bookchin in his seminal work Social Anarchism or Lifestyle Anarchism: An Unbridgeable Chasm (1997) ISBN 187317683X

Whereas Ian MacKaye (in the second recording of Out Of Step by Minor Threat) stressed that "this is not set of rules" Hardline is to be seen as a very strict ascetic doctrine.
Hardline was harshly criticized for their stance on sexuality i.e. maintaining that homosexuality, bisexualty(and even masturbation according to some Hardline literature), is unnatural and therefore wrong, their opposition to abortion, and the open promotion of violence as a method to protect animals and humans against further oppression. This stance was often misunderstood to promote violence against gays.

Hardline is as much indebted to anarchism and Abrahamic religion as it is Straight edge.

Hardline is an offshoot of straight edge, started by Al in boston in the late 80's. It was an even more intense version of straight edge. They were basically edge guys that would invade other's personal freedoms if they didn't agree with them. Kind of like hate edge.

"If Ian McKaye saw a guy drinking at an all ages show, he'd shoot him a dirty glance. If Al and his crew saw a guy drinking at an all ages show, they'd kick the shit out of you." -BBD vol. 2

Someone who was hardline was a person who believed in the complete liberation of all animals, human and non-human, through purity of living and violent and non-violent direct action against those whom they deemed to be "the oppressors." One who was hardline adopted a strict lifestyle based upon both vegan and straight edge principles. Hardline folks were also pro-life, and believed sex was strictly for procreation.

Hardline was a violent movement and officially ended in 1999 via a decision by the Hardline Central Comittee.

Hardline is an offshoot of straight edge, started by Al in boston in the late 80's. It was an even more intense version of straight edge. They were basically edge guys that would invade other's personal freedoms if they didn't agree with them. Kind of like hate edge.

They would listen to Hardcore music.

"If Ian McKaye saw a guy drinking at an all ages show, he'd shoot him a dirty glance. If Al and his crew saw a guy drinking at an all ages show, they'd kick the shit out of you." -BBD vol. 2

"i'm not a vegan and i have had sex,
so some hard-line kids tried to kick my ass,
if you're not like them they want to clean your clock ,
they're nothing but a bunch of jocks!
they're anti-choice, they're fascist youth,
their songs all sound like metal tunes!"
Anti-Flag from the song "Indie Sux, Hard-Line Sux, Emo Sux, You Suck!"